In the circulatory system for circulating blood in the bodies, the blood circulation efficiency and pattern closely relate to cardiovascular diseases. For example, an inefficient circulatory system imposes a load on the heart to increase the risk of cardiac failure. In order to investigate such hemodynamics, it is necessary to accurately obtain cardiac blood flow velocity. In particular, the pressure gradient for two points in the living body as important information for diagnosis is obtained by using valve regurgitation flow velocity, and therefore accurate flow velocity information focused on the valve regurgitation is required.
There is the Doppler measurement technique utilizing the Doppler effect as a method for obtaining blood flow velocity using ultrasonic waves. In the Doppler measurement technique, blood flow velocities are detected in all the regions irradiated with ultrasonic waves, and therefore the obtained velocity information (blood flow velocity distribution and blood flow velocity) has a certain width (range). Therefore, it is necessary to extract velocity information considered by a tester to be appropriate, but such extraction of velocity includes ambiguity, which leads to ambiguity of diagnosis.
Patent documents 1 and 2 disclose techniques for preventing errors of trace lines of Doppler waveform due to noises or signal aliasing in determining velocities on the basis of the Doppler waveform. Further, Patent document 3 discloses a technique of automatic tracing of the Doppler waveform utilizing a plurality of luminance levels lower than the maximum luminance level by predetermined degrees as the tracing levels, as for the basis of tracing of the Doppler waveform.